1. Technical Field
The present invention generally relates to switching systems for application services, and more particularly to a switching system for application services including a switching equipment which is coupled to terminals such as telephone sets with displays and an external application processor which is coupled to this switching equipment and stores programs for the application services.
2. Background Art
In a switching system for application services, a user makes access to an external application processor from a telephone set via a switching equipment by manipulating keys of the telephone set in a certain manner. Thus, the user can receive an application service which is provided by the external application processor. As examples of the application services, there are message display service, conference room reserving service, air conditioning control service, illumination control service and the like.
FIG. 1 generally shows an example of a conventional switching system for application services. In FIG. 1, the switching system for application services includes a digital telephone set 1 having a display, a line circuit 2, a switching equipment 3 and an external application processor 4. The telephone set 1 includes a handset 1A having transmitter/receiver functions, a display 1B for displaying various messages, a dial button group (key pad) 1C including a plurality of key buttons which are assigned numbers and predetermined symbols, and an application key button ID which is used when receiving an application service.
FIG. 2 shows the telephone set 1 and the line circuit 2 in more detail. In FIG. 2, a line terminating part 1E of the telephone set 1 separates and integrates audio signals and control signals. With regard to the audio signals, the signal transmission and reception are made between the line terminating part 1E and the handset 1A via a coder/decoder 1F and a telephone circuit 1G of the telephone set 1. With regard to the control signals, the signal transmission and reception are made between the line terminating part 1E and a controller 1H of the telephone set 1. The control signals include a signal for providing the application service.
The display 1B, the dial key button group 1C, the application key button 1D, a memory 1I and a hook switch 1J are connected to the controller 1H. The controller 1H can transmit signals to and receive signals from the display 1B, the dial key button group 1C, the application key button 1D, a memory 1I and a hook switch 1J.
The memory 1I stores programs which are required for processings in the controller 1H and transmission and reception data. The hook switch 1J detects an off-hook state and an on-hook state of the handset 1A.
The telephone set 1 is coupled to the switching equipment 3 via the line circuit 2. In other words, a driver 1K and a receiver 1L which are provided as transmitter/receiver part of the telephone set 1 are coupled to a corresponding receiver 2A and a corresponding driver 2B of the line circuit 2. The receiver 2A and the driver 2B are terminated at a line terminating part 2C. The audio signals and the control signals are separated and integrated in the line terminating part 2C, and the audio signals are transmitted to a network part 3A of the switching equipment 3. The control signals are transmitted to a common control unit 3B of the switching equipment 3 via an interface circuit 2D.
Frames which are transmitted between the digital telephone set 1 and the line circuit 2 have a structure in which audio bits V0 through V7 are inserted between a frame bit F and a control bit S, for example.
The external application processor 4 which stores a program for a predetermined application service is coupled to the common control unit 3B of the switching equipment 3. As application services, it is possible to consider message display service, air conditioning control service, illumination control service and the like, but the service is limited to one. That is, the external application processor 4 stores only the program for a specific application service.
Next, a description will be given of a procedure for carrying out the application service, by referring to FIG. 3. First, the user at the telephone set 1 pushes the application key button 1D, so that the application key button pushed information is transmitted from the telephone set 1 to the common control unit 3B of the switching equipment 3. When the common control unit 3B of the switching equipment 3 receives the application key button pushed information, an application service start is transmitted to the external application processor 4. Accordingly, the display information from the external application processor 4 related to a predetermined procedure, comments and the like is returned to the telephone set 1 via the common control unit 3B of the switching equipment 3. As a result, the above display information is displayed on the display 1B of the telephone set 1.
Thereafter, the user pushes the dial key button depending on the display information. The key information is transmitted to the external application processor 4 via the common control unit 3B of the switching equipment 3. Hence, it is possible to receive the application service which is provided by the external application processor 4.
Then, when the user pushes the application key button 1D, this information is transmitted from the telephone set 1 to the common control unit 3B of the switching equipment 3, and the common control unit 3B of the switching equipment 3 gives an application service connection release instruction.
However, according to such a conventional switching system for application services, the external application processor only stores the program for a specific application service. For this reason, when starting the external application processor from the telephone set so as to receive the application service, the application which is started is limited to one. Accordingly, there are problems in the switching system for application services from the point of view of added value.
As shown in FIG. 4, the display 1B includes a display memory 1B-1 for temporarily storing the display information, a display panel 1B-2 for displaying the display information, and a display controller 1B-3 for controlling the display. Only the data related to the present display content is stored in the display memory 1B-1. When new display information is input, the content of this memory 1B-1 is renewed by the new content. In FIG. 4, those parts which are the same as those corresponding parts in FIGS. 1 and 2 are designated by the same reference numerals, and a description thereof will be omitted.
Therefore, in the conventional switching system for application services, when a call is received from another line while the message for the application service is being displayed, the display information for call control such as the number of the caller is displayed on the display panel 1B-2 of the display 1B in place of the message display for the application service. As a result, the message display for the application service disappears, and there is a problem in that this message display cannot be displayed again.